Mainframe System Modernization: Reality Check

I just realized that the mainframe systems I support had been running for decades some even going back to the 1980’s. The interesting thing is there had been several hardware, operating system, database transaction processor and compiler upgrades, not to mention other system programs, and probably the greatest effort done on these was the Y2K conversion. Other than that, the most you probably have to do is some maintenance that takes a day to do. They all run in the production box without any tweaks to the system.